Spark plug



March 17, 1953 v DELANQ 2,632,132

SPARK PLUG Filed June 15, 1951 INVENTOR. JAMES 1K DEL/1N0 Patented Mar.17, 1953 UNITED STATES PATENT ()FFICE SPARK PLUG James Kendall Delano,Rye, N. Y. Application June 15, 1951, Serial No. 231,769

'7 Claims.

This invention relates to spark plugs, and particularly to a spark plugconstruction suitable for use in aircraft, engines at high altitudes.

In the type of service when planes frequently climb and fly at highaltitudes, the ignition system of the engine is affected, ,due to therarefication of the air. As the air pressure drops, the electricalleakage losses increase, and more voltage is required to provideadequate voltage at the spark plugs for the ignition. Unless this lossis prevented, the height to which a plane can climb becomes limited.

Various means have been employed to overcome this trouble. The principalremedies used today are the pressurized system where all the ignitionequipment including the magneto, the wires, etc. are kept under pressureand all high tension leads are placed in tubing and an air pump drivenfrom the engine keeps the pressure in the tubes at around groundair'press'ure.

Another system uses a low voltage magneto and supplies transformers tostep up the voltage to the plugs. The transformers are located veryclose to the engine plug so only a short wire is required to supply eachplug. This cuts down the losses that would result from long high voltageleads, but does not eliminate all the loss.

Another type of ignition employs a medium voltage magneto and enclosesits high voltage transformer in the body of the spark plug, but in turnthe terminals and parts permit air leakage due to contraction andexpansion and, where the pressure decreases during a flight, the reducedpressure allows the high voltage to flashover inside the plug.' Thisfiashover carbonizes the insulation and the plug ceases to function.

The transformer being very small so that it may be incorporated in aplug of this type is very limited in insulation on account of the smallwinding space, and it takes very little loss of ground air pressure tocause a breakdown. Great diificulties are met in trying to keep the wireterminals tight. In a plane flying from tropic to frigid temperatures orfrom ground to mountain heights, the expansion and contraction soonproduce leaks that allow the pressure to escape during flights at highelevation.

To overcome the foregoing difficulties, the present plug is provided, asdisclosed herein, that keeps its high voltage parts under high pressureat all times while the engine is operating.

One object of the invention is to provide an integrated spark plug, towhich only. low voltage energy need be, supplied, from asuitable lowvoltage s e and in wh h the hi h voltage 2 required for the operation orbreakdown of a spark gap will be generated by a suitable transformer inthe plug itself.

Another object of the invention is to provide a spark plug in which ahigh-pressure atmosphere is maintained during operation of the engine inwhich the spark plug is inserted.

Another object of the invention, bearing upon the functional andstructural features of the spark plug of this invention, will be morereadily appreciated on reference to the accompanying specification anddescription of the drawings in which:

Fig. 1 is a vertical elevational view of an assembled spark plug with aportion broken away to show the manner of connection of an externaldistributor lead to the input terminal thereof;

Fig. 2 is a vertical sectional view taken of the plug itself, takenalong the line 22 of the plug shown in Fig. 1;

Fig. 3 is a bottom end view of the plug of Fig. 1, showing thedisposition and construction of the spark ap electrodes;

Fig. 4 is a horizontal sectional view taken downward at a plane alongthe line 4-4 through the body of the plug, as, shown in Fig. 2.

As shown in the drawings, a spark plug it embodying the principles .ofthis invention comprises an input terminal -I I, a voltage transformerI? for stepping up a low input voltage to a high output voltage, and aspark gap l3 at the bottom end of the plug to be energized by such highvolt age. The foregoing elements are supported on the structure of theplug, which includes a base I 4 which serves as the foundation supportfor the entire plug. An enclosing shell 15 threads onto the base l4,against a pressure-sealing gasket l6, and serves to support thetransformer 52.

The base member I4 is shaped to include an externally threaded tubularsection I"! depending from a flanged main body portion 18 and having ashort co-axial tubular section is extending about the flanged bodyportion [8. The threaded tubular portion i-l serves as an insertion plugfor insertion in a correspondingly threaded hole in the wall ofacylinder head of an engine on which the spark plug is to be used. Theinsertion plug H has an inner cylindrical bore 2!, and at its lower endsupports'two electrodes 23 and 22 that constitute the cooperatingelectrodes of the spark gap or space between the two electrodes. Theelectrode 23 is supported directly at the lower end of the threadedtubular section ll, and consists of a disk-shaped element having anannular rim :4 nq a plurality .Of symmemtauy .dis-

posed polar portions 25 extending radially inward from the rim 24 to adistance closely spaced from the peripheral surface of the axialelectrode 22. The flanged main body portion E8 of the base member M isformed, as shown in Fig. 1, to constitute a hexagonal nut, to enable thespark plug to be manipulated by a wrench for tight insertion into acylinder head or for removal therefrom.

The plug base supporting member M is provided with a spherical seat 2?on its inner surface to receive a correspondingly spherically shapedboss 23 on an insulator 29 which serves as a partial support for thecenter or axial electrode 22 at the spark gap.

The upwardly extending threaded portion IQ of the base support i l isprovided with internal threads 3i and external threads 32. Theinternally threaded section accommodates and receives a lock nut 33which serves to clamp the insulator support 291 in fixed position uponthe base supporting member it, through the medium of two annular gaskets3d and 35 respectively disposed between the spherically-shaped insulatorboss 28 of the insulator body 28 and the seat 21, and between theinsulator body 23 and the lock nut 33.

The external threaded section 32 of the plug supporting member i laccommodates and receives the enclosing shell l5, which is showninternally threaded along the lower portion of The transformer l2comprises a spool lli of insulating material of ceramic or othersuitable material having a hollow tubular body M and two end flanges :32and d3 with a short co-axial tubular extension or apron id extendingcoaxially from the end flange 33. The upper spool flange E2 is providedwith a small hole 52-11 therethrough to accommodate a wire conductor 65then from the primary winding of the transformer to a terminal anchorscrew M5 which serves also to anchor a terminal spring 4.! in positionat the top of the spool to engage the undersurface of the input terminalll. v

The lower spool flange 13 is similarly provided with a hole attherethrough to accommodate a conductor 43 leading from a primaryterminal of the transformer winding to a grounding copper washer 5i)resting on a threaded lock nut 5|. The lock nut 51 is shown providedwith openings 53 to receive a spanner wrench by means of which the locknut 55 may be tightened or loosened, upon insertion in or removal fromthe enclosing shell it.

By means of the lock nut 5i the transformer spool assembly may bepressed home tightl with the contact spring ll pressing against theunder surface of the input terminal i l, thereby to clamp thetransformer tightly in flxed position.

The transformer i2 is provided with a primary winding 55 and a secondarywinding 56. The primary winding is of a relatively small number ofturns, and the secondary winding 55 has a relatively large number ofturns, as is well understood in the art, in order to provide a stepuptransforming action whereby a current of low voltage supplied to theprimary winding will induce a high voltage in the secondary winding 56,in accordance with the ratio of the number of turns. The windings 55 and56 are separated by an insulating sleeve 51.

The circuit of the primary winding 55 proceeds from the input terminal Hthrough the contact spring ll and thence through the winding 55 itselfto the other terminal 4 of that winding, which is then grounded on thecopper washer 5d, which is in direct metallic contact and thereforeelectrical contact with the lock nut 58, and thence through the shell 15down to the body of the plug supporting member M, which will be groundedon the engine block in which it will be inserted for operation. Thesecondary winding 56 has one terminal also connected to the groundinglead is in order to be grounded on the metallic structure of the plug.The other terminal of the secondary winding, which is the hot terminal,is connected to the magnetic iron core 58 of the transformer to providea terminal to which electrical and mechanical contact may be readily andeasily made during assembly in order to provide an electrical connectionfrom the hot terminal of the secondary winding to the axial electrode 22at the spark gap.

The electrical connection from the core of the transformer is made tothe axial electrode 22 of the spark gap by means of a simple assemblyconsisting of a cylindrical rod cc axially recessed at its upper end toaccommodate a metallic conducting spring Si disposed to seat between thelower end of the core 53 of the transformer and a floating contact andvalve 52 seated in the bottom of the recess in the upper end of the rodfit, in order to establish an electrical contact between the core 58, asone electrode terminal of the secondary winding, the rod to which iselectrically connected at its lower end to the axial spark gap electrode22, thereby providing an electrical connection from the high voltageterminal of the secondary winding to the spark gap electrode 22. The rodEd has a central axial narrow passage (53 throughout its length that isnormally closed by the contact valve 62 by pressure of the spring El fora purpose to be eX-i plained below.

Since the rod es must carry the high voltage from the secondary windingof the transformer to the axial electrode 22 of the spark gap, the rod60 constitutes a high voltage conductor and is supported in theinsulator 29, to insulate that high, voltage connection from the commongrounded metallic structure of the plug. The upper end of the insulator29 is confined within the depending tubular extension or apron 4 3 whichserves to insulate that conductor further from the lock nut 5i.

By means of the construction that is shown, the input terminal H and thetransformer unit I2, together with the copper washer 59, are tightlyassembled as one unit in the upper part of the shell 15 by means of thetightened lock nut 5i. The insulator 29 is assembled on the plugsupporting member M by the threaded lock nut 33 together with the twosealing gaskets 34 and 35, to position the two electrodes 22 and 2-3 ofthe spark gap in suitable symmetrical relationship. The upper and thelower parts of the plug may then be easily and readily assembled bythreading the enclosing shell it) onto the outer threaded portion 32 ofthe upwardly extending tubular portion it of the base plug i4, since theelectrical connection will be established and maintained by theconducting compression spring 6!, between the core as a terminal of thesecondary winding and the rod 613 as a terminal for the connection tothe spark gap terminal 22.

The input terminal H is suitably tightly locked in position on a reducedhead portion 64 of the shell I5, being suitably insulated by insulatingtubes 65 and 66 and the annular seating washer 6'1.

When an energy pulse is fed from the external ignition control system tothe input terminal l! of the plug, that pulse will generate acorrespondingly high voltage pulse in the secondary Winding of thetransformer, and that high voltage pulse will be transmitted to theaxial electrode 22 at the spark gap. The high voltage between the twoterminals at the spark gap will cause an arc to be made across the smallgap, which will ignite the explosive mixtur compressed in the cylinderand existing between the electrodes of the spark gap. The heat from thatignition will be imparted to the small volume of explosive mixture inchamber 2 l, with consequent expansion of the quantity of that mixturein the chamber 2!. The quantity of the mixture in chamber 2! will thusbe heated before the surrounding mixture in the cylinder, withconsequent expulsion movement of some of the explosive mixture in thechamber 2!. Th expulsion movement moves the spark slightly for ward andoutward into the compressed mixture in the cylinder and thereby assuresincreased heat exchange between the arc and the compressed mixture inthe cylinder.

At high altitudes the low pressure rarefied atmcsphere has lessinsulating value than norma pressure atmosphere at sea level.

In order that the transformer will not break down in the high altitudesand cause an elec tric leakage to be effected between turns of thetransformer windings and the enclosed shell, gas pressure is suppliedinto the enclosing shell i5, from the engine cylinder in which the sparkplug is inserted. Such gas pressure enters the enclosing shell through asmall hole 58 in the spark gap electrode 22 that communicates with thesmall hole 63 in the rod 60. The hole 53 in the rod is normally closedby contact 62 which serves as a valve element under the biasing force ofspring 5!. The valve seals off any pressure that may have passed thevalve and entered the shell IE to immerse transformer Ml. Whenever anypressure within this space is lost, it will be replenished by furthermovement of gas under pressure past the combination contact and valveelement 62 against compression spring 51. It will thus be seen thatthrough this means, even though the aircraft is taken into the rarefiedatmosphere, the transformer will be kept under pressure by the gasesfrom the engine, and will be protected against leakage.

The diameter of hole 63 in the rod 60 is too small to permit flamepropagation up into the rod. Moreover, after a few ignitions, the hole63 contains sufficient products of combustion to inhibit a producingcondition. Such pressure mixtures from the cylinder pass up through thehole 63 and then through a small gap 69, between the upper end of theinsulator bodv 29 and the adjacent lower surface of the bottom flange 53of the transformer supporting s ool, into the chamber 79 between thelock nut 5i and the lock nut 33. From that chamber 19, the pressuregases seen up into the upper chamber around the transformer and keep theatmosphere around the transformer at high pressure.

Due to the small unoccupied space inside of the enclosure there is verylittle capacity for the gases to fill.

The check valves 62 and spring 6! are set so that a firing stroke onlywill open the valve. At

this instant the gasoline vapor is or has been ig-. nited, so verylittle raw gas enters the opening in the end of the electrode. As thefiring pres! sure drops in the engine cylinder, the check valve 62 willhave closed and trapped ample pressure in the plug casing. If the plugis tight, the valve will remain closed most of the time, opening only tokeep the pressure up in the casing.

With the high pressure in the plug, there is no danger from electricbreakdown in the insulation. The low pressure input terminal H is madecone-shaped so that the inside pressure seals it tightly against themating insulator cone 65.

The transformer is mounted on a ceramic spool, as described, and thesecondary is wound next to the cone, with layers. The turns of primaryand secondary are balanced for high frequency tuned circuit operation,and may be of fewer turns than are ordinary type ignition coils. A flux,guiding split shield 13 is placed preferably to encircle the entiretransformer spool so that the coil fiux will take its path through theshield rather than induce eddy currents in the casing H5. The shield issubstantially a cylinder with a longitudinal gap it to prevent eddycurrents in the shield, and is preferably insulated from the enclosingshell I 5 by an insulating varnish or thin paper which is adequate forthat purpose. The gap i i in the shield should preferably be oblique toits radius so the shield will provide a metal enclosure throughout theentire circular angle around the axis.

Simple electrical connections may be made to the upper input terminal Hby means of a simple pressure disc 75 connected to the end of a wireconductor 15, leading from the ignition system and supported on aninsulating disc plate ll that is secured to and supported by a pipesection '55 arranged to be tightly threaded onto the threaded head ofthe plug shell by means of a threaded nut 19.

By means of the construction illustrated herein a simple integratedspark plug is provided which can be simply and easily constructed andassembled to generate a high voltage directly at the spark plug wherethe high voltage is desired for use. The external ignition systemnecessary to excite the plug may, therefore, be completely of a lowvoltage system with a consequent elimination of need for highvoltagecables and insulating supports.

Moreover, the proper operation of the spark plug is assured bymaintaining a locally pressurized atmosphere within each spark plug toprevent leakage that would result from a low pressure atmosphere.

This invention is not limited specifically to the exact details ofconstruction that are shown since various simple modifications may bemade therein without departing from the spirit and scope of theinvention, as set forth in the ap pended claims.

What is claimed is:

l. A spark plug comprising a base supporting member adapted to be fittedinto an engine head, an enclosing shell secured to the base member andhaving a low tension terminal at its upper end, a transformer having acontact engaging with the low tension terminal of the shell and havingprimary and secondary windings, the primary winding being connected atone end to the transformer contact, the other end of said primary beinggrounded along with one end of the secondary winding to the shell, aspool containing a magnetic core connected to the other end of thesecondary winding connected to said magnetic core, a hollow insulatingmember and combined sealing and clamp means for securing said insulatingmember to said base supporting member, a rod extending through theinsulating member having an enlarged opening in the upper end; said rodabutting the lower end of the transformer, a conductor compressionspring within the enlarged opening of the upper end of the rod engagingat its upper end the core of the transformer, a metal contact element insaid enlarged opening in the upper end of the rod and said conductorcompression spring urging said contact into the bottom of the enlargedopening within the rod, and electrodes connected respectively to thelower end of the rod and to the base supporting member to provide aspark gap therebetween, said rod and the electrode thereon having asmall hole communicating from the lower end of the electrode to thebottom of the large opening in the upper end of the rod whereby gaspressure from the engine may be delivered upwardly into the shell andabout the transformer whereby to inhibit voltage leakage between turnsof the windings and between the transformer and the shell and saidcontact element within the large opening in the rod being urged by thespring therein and serving as a valve element to withhold the gas withinthe transformer space under predetermined pressure and to allow thespace to be replenished with gas pressure upon the gas entrapped thereinbeing diminished.

2. A spark plug comprising a shell housing, a step-up transformerenclosed therein, an input terminal extending through the housing tosupply low voltage to the transformer, a pair of spark gap terminalssupported from the housing for insertion into the compression region ofan engine cylinder, means for supplying high voltage from thetransformer to the spark gap, and means for admitting pressure gasesfrom a region in the neighborhood of the spark gap into 7 8 the housingto maintain a high pressure atmosphere around the transformer and withinthe housing during operation of the spark plug.

3. A spark plug, as in claim 2, in which the pressure admitting meansconsists of a oneway valve.

4. A spark plug, as in claim 2, comprising a metallic tubular conduitfor electrically connecting the transformer secondary to one spark plugterminal and serving as the means for admitting and conducting thepressure gases from the region of said spark plug terminal into thehousing to immerse the transformer.

5. A spark plug, as in claim 4, in which a oneway valve is disposed inthe tubular conduit to control the admission of pressure gases into thehousing.

6. In a spark plug having a pair of spark gap terminals and atransformer to be supplied with low voltage and to supply stepped upvoltage to the spark gap terminals, and a housing for enclosing thetransformer, the method of opera ing the plug while it is in service onan engine which comprises supplying pressure gases from the engine tothe housing, to immerse the transformer in an atmosphere at a pressurehigher than ambient pressure outside the plug.

7. The method set forth in claim 6 including the step of periodicallyreplenishing the pressure upon any diminution by leakage from apredetermined pressure within the housing.

JAMES KENDALL DELANO.

REFERENCES CITED The following references are of record in the fileof-this patent:

UNITED STATES PATENTS Number Name Date 2,266,614 Robinson Dec. 16, 19412,461,098 Weatherly Feb. 3, 1949 2,482,884 Tognola Sept. 27, 19492,575,140 Smith Nov. 13, 1951

